Dual-chamber pacemaker system for simultaneous bi-chamber pacing and sensing

ABSTRACT

A method of pacing opposing chambers of a heart with a pacing system is provided. The pacing system comprises a first bipolar medical electrical lead having at least one first electrode configured for positioning in a first opposing chamber of the heart, a second bipolar medical electrical lead having at least one second electrode configured for positioning in a second opposing chamber of the heart, an implantable pulse generator operably connected to the first and second bipolar medical electrical leads. The implantable pulse generator further comprises a hermetically sealed housing capable of serving as a can electrode. The method designates a primary electrode configuration by selecting a cathode and an anode from either the first electrode, second electrode, or the can. Selection of the cathode is based on a comparison of thresholds measured in each chamber. Systems, programs and devices using the method are also provided.

This application is a continuation of application Ser. No. 10/024,226,filed Dec. 21, 2001 now U.S. Pat. No. 6,950,701, now allowed.

FIELD OF THE INVENTION

The present invention relates to the field of implantable medicaldevices, and, more particularly, to dual-chamber cardiac pacing systemsthat are capable of switching electrode configurations when two unipolarleads are disposed in opposing heart chambers (i.e., left and rightatria or left and right ventricles).

BACKGROUND OF THE INVENTION

Tachyarrhythmias are episodes of high-rate cardiac depolarizations.Tachyarrhythmias may occur in one chamber of the heart or may bepropagated from one chamber to another. Some tachyarrhythmias aresufficiently high in rate to compromise cardiac output from thechamber(s) affected, leading to loss consciousness or death, in the caseof ventricular fibrillation or weakness and dizziness in the case ofatrial fibrillation. Atrial fibrillation is often debilitating, due tothe loss of atrial cardiac output, and may sometimes lead to ventricularfibrillation.

Generally, fibrillation may be terminated by administering high energylevel cardioversion/defibrillation shocks or pulses until thefibrillation is terminated. For example, in the context of implantableanti-arrhythmia devices, these pulses may be applied by means of largesurface area electrodes on or in the chamber to be defibrillated.However, the high energy level pulses are often sufficient to cause painto the patient. Thus, it would be desirable to prevent or decrease theoccurrence of atrial fibrillation without the delivery of high energylevel pulses.

Some exploration has, therefore, been made in the use of pacing levelpulses, which stimulate the cardiac tissue at much lower levels thandefibrillation pulses, to terminate atrial fibrillation.

Implantable pulse generators (IPGs) that deliver pacing level pulses arewell known in the art. These IPGs may deliver pulses to one or morechambers of the heart. Some of these devices provide pacing stimuli tothe heart at a predetermined rate. The stimuli may be applied at a fixedrate, on demand, at a rate synchronized to atrial activity or at a ratesynchronized to ventricular activity. This type of pacing function mayalso be used in other devices such as, for example, implantablecardioverter defibrillators (ICDs) or in external pacemakers. Most IPGsinclude sense amplifier circuitry for detecting intrinsic cardiacelectrical activity. Some IPGs also include sensors or sensingelectrodes to determine reliably the heart rate (or pacing rate) in aheart under different conditions. Some IPGs are dual-chamber, havingboth atrial and ventricular leads. These IPGs have a unipolar lead inthe ventricle and a unipolar lead in the atrium.

To deliver pacing pulses of sufficient magnitude to have the desiredeffect, it may be desirable to stimulate or sense more than one chamberof the heart simultaneously. This may be desirable, for example, becausethe simultaneous stimulation in opposing chambers results in stimulationpulses of higher amplitude or duration. This may also be desirablebecause stimulation across opposing chambers of the heart stimulates adesired location of tissue that is more difficult to stimulate acrossonly one chamber of the heart. In standard IPGs, a minimumatrio-ventricular delay makes such simultaneous stimulation difficult orimpossible. That is, there is a minimum delay between the time a firstchamber, for example the left atria, is stimulated/sensed and the timethe second chamber, for example the right atria, is stimulated/sensed.

It would also be desirable to provide stimulation to opposing chambersof the heart using standard programming settings and existing fixedconnections in an IPG without the addition of further splitters andadapters.

It would also be desirable to provide switchable configurations ofelectrodes disposed in opposing atria or ventricles of the heart.

Thus, a need exists in the medical arts for simultaneous stimulationand/or sensing of opposing chambers of a heart.

Several methods have been proposed in the prior art for improving animplantable device's ability to administer pacing pulses simultaneouslyto more than one chamber of a heart.

For example, U.S. Pat. No. 5,514,161 to Limousin, entitled “Methods andApparatus for Controlling Atrial Stimulation in a Double Atrial TripleChamber Cardiac Pacemaker”, hereby incorporated by reference in itsentirety, discloses a double atrial triple chamber pacemaker, whichprovides simultaneous stimulation to both atria through the provision ofa Y connector.

U.S. Pat. No. 5,757,970 to Pouvreau, entitled “System, Adaptor andMethod to Provide Medical Electrical Stimulation” discloses an adaptorthat permits a single channel of stimulation to be split and provided totwo areas of the heart by adjusting the amplitude of the stimulationpulses.

The article “Permanent Multisite Cardiac Pacing” by Barold, et al. inthe journal PACE discloses the use of a Y connector to split a standardbipolar output into anode and cathode electrodes.

The article “Hemodynamic Benefits of Permanent Atrial ResynchronizationPatients with Advanced Inter Atrial Blocks, paced DDD Mode” by Daubertet al. in the journal PACE discloses the use of a bifurcated electrodeto pace between the right atrium and the coronary sinus in order to paceboth atria simultaneously.

As discussed above, the most pertinent prior art patents are shown inthe following table:

TABLE 1 Prior Art Publications Patent No. Date Inventor(s) U.S. Pat. No.5,514,161 May 7, 1996 Limousin U.S. Pat. No. 5,757,970 Aug. 25, 1998Pouvreau Barold et al. (November 1997) “System, Adaptor and Method toProvide Medical Electrical Stimulation” PACE, Vol. 20, pages 2725-2729.Daubert et al. (April 1997) “Hemodynamic Benefits of Permanent AtrialResychronization Patients with Advanced Inter Atrial Blocks, paced DDDMode” PACE, Vol. 14, Part II, page 640, #130.

All the publications listed in Table 1 are hereby incorporated byreference herein in their respective entireties. As those of ordinaryskill in the art will appreciate readily upon reading the Summary of theInvention, the Detailed Description of the Preferred Embodiments and theclaims set forth below, many of the devices and methods disclosed in thepatents of Table 1 may be modified advantageously by using the teachingsof the present invention.

SUMMARY OF THE INVENTION

The present invention is therefore directed to providing a method andsystem for simultaneously stimulating and/or sensing opposing chambersof the heart. The system of the present invention overcomes at leastsome of the problems, disadvantages and limitations of the prior artdescribed above, and provides a more efficient and accurate means ofstimulating opposing chambers of a heart.

The present invention has certain objects. That is, various embodimentsof the present invention provide solutions to one or more problemsexisting in the prior art respecting the pacing of cardiac tissue. Thoseproblems include, without limitation: (a) difficulty in simultaneousstimulation of opposing chambers of the heart; (b) need to addsplitters, adapters and additional circuitry to an existing IPG in orderto accomplish simultaneous stimulation; (c) difficulty in determiningappropriate sensing configurations using one or more leads; (d)difficulty in optimizing contractions induced in an opposing chamber ofthe heart; (e) difficulty in varying cathode and anode functions ofelectrodes disposed in opposing chambers, (f) difficulty in testing anddetermining which chamber of the heart provides the lowest pacingthreshold; (g) difficulty in configuring electrodes already disposed inopposing chambers of the heart to take advantage of the lowest pacingthreshold; (h) need to change circuitry or software/firmware in order toswitch electrode configurations.

In comparison to known pacing techniques, various embodiments of thepresent invention provide one or more of the following advantages: (a)ability to provide simultaneous stimulation to opposing chambers of aheart; (b) ability to provide bi-atrial or bi-ventricular stimulationwithout an atrio-ventricular delay; (c) ability to reversibly select ananode electrode and a cathode electrode for simultaneous stimulationwithout removing either electrode from its existing connection; (d)ability to switch and/or select electrode configurations of electrodesalready disposed in opposing chambers of the heart; (e) ability toswitch and/or select polarity of a given electrode already disposed in achamber of the heart; (f) ability to optimize hemodynamics of inducedcontractions in an opposing chamber of the heart; (g) ability to testand determine the chamber having the lowest pacing threshold andconfigure the electrodes to take advantage of the lowest pacingthreshold without using specialized lead adapters; and (h) ability totest and determine the chamber having the lowest pacing threshold andconfigure the electrodes to take advantage of the lowest pacingthreshold without removing the leads from the connector block andre-inserting them in different connector receptacles.

Some embodiments of the present invention include one or more of thefollowing features: (a) an IPG capable of providing bi-atrial orbi-ventricular stimulation without an atrio-ventricular delay; (b) anIPG capable of reversibly switching anode and cathode electrodes forsimultaneous stimulation without additional adapters or connectors; (c)an IPG capable of testing opposing chambers to determine which chamberhas the lowest pacing threshold and of configuring the electrodes totake advantage of the lowest pacing threshold; (d) an IPG in which thepolarity of various electrodes is selectable and/or switchable; (e) anIPG capable of providing staggered stimulation to optimize hemodynamicsof induced contractions (f) methods of reversibly selecting an anodeelectrode and a cathode electrode for simultaneous stimulation withoutremoving either electrode from its existing connection; (g) methods ofswitching and/or selecting electrode configurations of electrodesalready disposed in opposing chambers of the heart; (h) methods ofswitching and/or selecting polarity of a given electrode disposed in achamber of the heart; and (i) methods of optimizing hemodynamics ofinduced contractions in an opposing chamber of the heart.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, and other objects, advantages and features of the presentinvention will be more readily understood from the following detaileddescription of the preferred embodiments thereof, when considered inconjunction with the drawings, in which like reference numerals indicateidentical structures throughout the several views, and wherein:

FIG. 1 is a schematic view of one embodiment of an implantable medicaldevice in situ, made in accordance with the present invention;

FIG. 2 is another schematic view of an embodiment of the implantablemedical device of FIG. 1, made in accordance with the present invention;

FIG. 3 is a block diagram illustrating components of an embodiment ofthe implantable medical device of FIG. 1, made in accordance with thepresent invention;

FIG. 4 is a schematic view of another embodiment of an implantablemedical device, made in accordance with the present invention;

FIG. 5 is a block diagram illustrating components of an embodiment ofthe implantable medical device of FIG. 4, made in accordance with thepresent invention;

FIG. 6 is a schematic view of one embodiment of an implantable medicaldevice for comparison with the present invention;

FIG. 7 is a schematic view illustrating components of one embodiment ofan implantable medical device, made in accordance with the presentinvention;

FIG. 8 is a schematic view illustrating one configuration of thecomponents of the embodiment of the implantable medical device of FIG.7;

FIG. 9 is a schematic view illustrating one configuration of thecomponents of the embodiment of the implantable medical device of FIG.7;

FIG. 10 is a schematic view illustrating one configuration of thecomponents of the embodiment of the implantable medical device of FIG.7;

FIG. 11 is a schematic view illustrating one configuration of thecomponents of the embodiment of the implantable medical device of FIG.7;

FIG. 12 is a flow diagram of one embodiment of a method for stimulatinga heart in accordance with the present invention;

FIG. 13 is a flow diagram of another embodiment of a method forstimulating a heart in accordance with the present invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

It is to be understood that the terms “IPG” and “IMD”, as employed inthe specification and claims hereof, connote an implantable medicaldevice capable of delivering electrical stimuli to cardiac tissue, andinclude within their scope pacemakers, PCDs, ICDs, etc.

FIG. 1 is a simplified schematic view of one embodiment of implantablemedical device (“IMD”) 10 of the present invention. The IMD 10 shown inFIG. 1 is a pacemaker comprising at least one of pacing and sensingleads 16 and 18 attached to hermetically sealed enclosure 14 andimplanted near human or mammalian heart 8. Pacing and sensing leads 16and 18 sense electrical signals attendant to the depolarization andre-polarization of the heart 8, and further provide pacing pulses forcausing depolarization of cardiac tissue in the vicinity of the distalends thereof. Sensing leads 16, 18 may serve, for example, as sensors tosense an atrial response (such as an atrial sensed response or an atrialpulse signal) in accordance with the present invention. One or both ofleads 16, 18 may also serve to sense a ventricular response inaccordance with the present invention. Leads 16 and 18 may have unipolaror bipolar electrodes disposed thereon, as is well known in the art.Examples of IMD 10 include implantable cardiac pacemakers disclosed inU.S. Pat. No. 5,158,078 to Bennett et al., U.S. Pat. No. 5,312,453 toShelton et al. or U.S. Pat. No. 5,144,949 to Olson, all of which arehereby incorporated by reference, each in their respective entireties.

FIG. 2 shows connector module 12 and hermetically sealed enclosure 14 ofIMD 10 located in and near human or mammalian heart 8. Atrial andventricular pacing leads 16 and 18 extend from connector header module12 to the right atrium and ventricle, respectively, of heart 8. Atrialelectrodes 20 and 21 disposed at the distal end of atrial pacing lead 16may be located in the right atrium. Alternatively, in accordance withthe present invention, at least one of atrial electrodes 20, 21 may belocated in the left atrium. In one embodiment of the invention, one orboth of atrial electrodes 20, 21 may serve as sensors to sense an atrialresponse (such as an atrial sensed response or an atrial pulse signal)in accordance with the present invention. Ventricular electrodes 28 and29 at the distal end of ventricular pacing lead 18 are located in theright ventricle. Alternatively, in accordance with the presentinvention, at least one of the ventricular electrodes 28, 29 may belocated in the left ventricle. One or both of ventricular electrodes 28,29 may also serve to sense a ventricular response in accordance with thepresent invention.

FIG. 3 shows a block diagram illustrating the constituent components ofIMD 10 in accordance with one embodiment of the present invention, whereIMD 10 is a pacemaker having a microprocessor-based architecture. IMD 10is shown as including activity sensor or accelerometer 11, which may bean accelerometer bonded to a hybrid circuit located inside enclosure 14.Activity sensor 11 typically (although not necessarily) provides asensor output that varies as a function of a measured parameter relatingto a patient's metabolic requirements. For the sake of convenience, IMD10 in FIG. 3 is shown with lead 18 only connected thereto; similarcircuitry and connections not explicitly shown in FIG. 3 apply to lead16.

IMD 10 in FIG. 3 may be programmable by means of an external programmingunit (not shown in the Figures). One such programmer is the commerciallyavailable Medtronic Model 9790 programmer, which is microprocessor-basedand provides a series of encoded signals to IMD 10, typically through aprogramming head which transmits or telemeters radio-frequency (RF)encoded signals to IMD 10. Such a telemetry system is described in U.S.Pat. No. 5,312,453 to Wyborny et al., hereby incorporated by referenceherein in its entirety. The programming methodology disclosed in U.S.Pat. No. 5,312,453 to Wyborny et al., is identified herein forillustrative purposes only. Any of a number of suitable programming andtelemetry methodologies known in the art may be employed so long as thedesired information is transmitted to and from the pacemaker.

As shown in FIG. 3, lead 18 is coupled to node 50 in IMD 10 throughinput capacitor 52. Activity sensor or accelerometer 11 may be attachedto a hybrid circuit located inside hermetically sealed enclosure 14 ofIMD 10. The output signal provided by activity sensor 11 is coupled toinput/output circuit 54. Input/output circuit 54 contains analogcircuits for interfacing to heart 8, activity sensor 11, antenna 56 andcircuits for the application of stimulating pulses to heart 8.Accordingly, the rate at which heart 8 is stimulated or beatsspontaneously without stimulation may be controlled and/or monitoredusing software-implemented algorithms or pacing rate functions stored inmicrocomputer circuit 58.

Microcomputer circuit 58 may comprise on-board circuit 60 and off-boardcircuit 62. Circuit 58 may correspond to a microcomputer circuitdisclosed in U.S. Pat. No. 5,312,453 to Shelton et al., herebyincorporated by reference herein in its entirety. On-board circuit 60may include microprocessor 64, system clock circuit 66 and on-board RAM68 and ROM 70. Off-board circuit 62 may comprise a RAM/ROM unit.On-board circuit 60 and off-board circuit 62 are each coupled by datacommunication bus 72 to digital controller/timer circuit 74.Microcomputer circuit 58 may comprise a custom integrated circuit deviceaugmented by standard RAM/ROM components.

Electrical components shown in FIG. 3 are powered by an appropriateimplantable battery power source 76 in accordance with common practicein the art. For the sake of clarity, the coupling of battery power tothe various components of IMD 10 is not shown in the Figures. Antenna 56is connected to input/output circuit 54 to permit uplink/downlinktelemetry through RF transmitter and receiver telemetry unit 78. By wayof example, telemetry unit 78 may correspond to that disclosed in U.S.Pat. No. 4,566,063, issued to Thompson et al., hereby incorporated byreference herein in its entirety, or to that disclosed in theabove-referenced '453 patent to Wyborny et al. It is generally preferredthat the particular programming and telemetry scheme selected permit theentry and storage of cardiac rate-response parameters. The specificembodiments of antenna 56, input/output circuit 54 and telemetry unit 78presented herein are shown for illustrative purposes only, and are notintended to limit the scope of the present invention.

Continuing to refer to FIG. 3, V_(REF) and Bias circuit 82 may generatestable voltage reference and bias currents for analog circuits includedin input/output circuit 54. Analog-to-digital converter (ADC) andmultiplexer unit 84 digitizes analog signals and voltages to provide“real-time” telemetry intracardiac signals and battery end-of-life (EOL)replacement functions. Operating commands for controlling the timing ofIMD 10 are coupled by data communication bus 72 to digitalcontroller/timer circuit 74, where digital timers and counters establishthe overall escape interval of the IMD 10 as well as various refractory,blanking and other timing windows for controlling the operation ofperipheral components disposed within input/output circuit 54.

Digital controller/timer circuit 74 may be coupled to sensing circuitry,including sense amplifier 88, peak sense and threshold measurement unit90 and comparator/threshold detector 92. Circuit 74 may further becoupled to electrogram (EGM) amplifier 94 for receiving amplified andprocessed signals sensed by lead 18. Sense amplifier 88 amplifies sensedelectrical cardiac signals and provides an amplified signal to peaksense and threshold measurement circuitry 90, which in turn provides anindication of peak sensed voltages and measured sense amplifierthreshold voltages on multiple conductor signal path 67 to digitalcontroller/timer circuit 74. An amplified sense amplifier signal is thenprovided to comparator/threshold detector 92. By way of example, senseamplifier 88 may correspond to that disclosed in U.S. Pat. No. 4,379,459to Stein, hereby incorporated by reference herein in its entirety.

The electrogram signal provided by EGM amplifier 94 is employed when IMD10 is being interrogated by an external programmer to transmit arepresentation of a cardiac analog electrogram. See, for example, U.S.Pat. No. 4,556,063 to Thompson et al., hereby incorporated by referenceherein in its entirety. Output pulse generator 96 provides pacingstimuli to patient's heart 8 through coupling capacitor 98 in responseto a pacing trigger signal provided by digital controller/timer circuit74 each time the escape interval times out, an externally transmittedpacing command is received or in response to other stored commands as iswell known in the pacing art. By way of example, output amplifier 96 maycorrespond generally to an output amplifier disclosed in U.S. Pat. No.4,476,868 to Thompson, hereby incorporated by reference herein in itsentirety.

The specific embodiments of input amplifier 88, output amplifier 96 andEGM amplifier 94 identified herein are presented for illustrativepurposes only, and are not intended to be limiting in respect of thescope of the present invention. The specific embodiments of suchcircuits may not be critical to practicing some embodiments of thepresent invention so long as they provide means for generating astimulating pulse and are capable of providing signals indicative ofnatural or stimulated contractions of heart 8.

In some preferred embodiments of the present invention, IMD 10 mayoperate in various non-rate-responsive modes, including, but not limitedto, DDD, DDI, VVI, VOO and VVT modes. In other preferred embodiments ofthe present invention, IMD 10 may operate in various rate-responsive,including, but not limited to, DDDR, DDIR, VVIR, VOOR and VVTR modes.Some embodiments of the present invention are capable of operating inboth non-rate-responsive and rate responsive modes. Moreover, in variousembodiments of the present invention IMD 10 may be programmablyconfigured to operate so that it varies the rate at which it deliversstimulating pulses to heart 8 only in response to one or more selectedsensor outputs being generated. Numerous pacemaker features andfunctions not explicitly mentioned herein may be incorporated into IMD10 while remaining within the scope of the present invention.

The present invention is not limited in scope to single-sensor ordual-sensor pacemakers, and is not limited to IMDs comprising activityor pressure sensors only. Nor is the present invention limited in scopeto single-chamber pacemakers, single-chamber leads for pacemakers orsingle-sensor or dual-sensor leads for pacemakers. Thus, variousembodiments of the present invention may be practiced in conjunctionwith more than two leads or with multiple-chamber pacemakers, forexample. At least some embodiments of the present invention may beapplied equally well in the contexts of single-, dual-, triple- orquadruple-chamber pacemakers or other types of IMDs. See, for example,U.S. Pat. No. 5,800,465 to Thompson et al., hereby incorporated byreference herein in its entirety, as are all U.S. Patents referencedtherein.

IMD 10 may also be a pacemaker-cardioverter-defibrillator (“PCD”)corresponding to any of numerous commercially available implantablePCDs. Various embodiments of the present invention may be practiced inconjunction with PCDs such as those disclosed in U.S. Pat. No. 5,545,186to Olson et al., U.S. Pat. No. 5,354,316 to Keimel, U.S. Pat. No.5,314,430 to Bardy, U.S. Pat. No. 5,131,388 to Pless and U.S. Pat. No.4,821,723 to Baker et al., all of which are hereby incorporated byreference herein, each in its respective entirety.

FIGS. 4 and 5 illustrate one embodiment of IMD 10 and a correspondinglead set of the present invention, where IMD 10 is a PCD. In FIG. 4, theventricular lead takes the form of leads disclosed in U.S. Pat. Nos.5,099,838 and 5,314,430 to Bardy, and includes an elongated insulativelead body 1 carrying three concentric coiled conductors separated fromone another by tubular insulative sheaths. Located adjacent the distalend of lead 1 are ring electrode 2, extendable helix electrode 3 mountedretractably within insulative electrode head 4 and elongated coilelectrode 5. Each of the electrodes is coupled to one of the coiledconductors within lead body 1. Electrodes 2 and 3 may be employed forcardiac pacing and for sensing ventricular depolarizations. At theproximal end of the lead is bifurcated connector 6, which carries threeelectrical connectors, each coupled to one of the coiled conductors.Defibrillation electrode 5 may be fabricated from platinum, platinumalloy or other materials known to be usable in implantabledefibrillation electrodes and may be about 5 cm in length.

The atrial/SVC lead shown in FIG. 4 includes elongated insulative leadbody 7 carrying three concentric coiled conductors separated from oneanother by tubular insulative sheaths corresponding to the structure ofthe ventricular lead. Located adjacent the J-shaped distal end of thelead are ring electrode 9 and extendable helix electrode 13 mountedretractably within an insulative electrode head 15. Each of theelectrodes is coupled to one of the coiled conductors within lead body7. Electrodes 13 and 9 may be employed for atrial pacing and for sensingatrial depolarizations. Elongated coil electrode 19 is provided proximalto electrode 9 and coupled to the third conductor within lead body 7. Inone embodiment of the invention, electrode 19 is 10 cm in length orgreater and is configured to extend from the SVC toward the tricuspidvalve. In one embodiment of the present invention, approximately 5 cm ofthe right atrium/SVC electrode is located in the right atrium with theremaining 5 cm located in the SVC. At the proximal end of the lead isbifurcated connector 17, which carries three electrical connectors, eachcoupled to one of the coiled conductors.

The coronary sinus lead shown in FIG. 4 assumes the form of a coronarysinus lead disclosed in the above cited '838 patent issued to Bardy, andincludes elongated insulative lead body 41 carrying one coiled conductorcoupled to an elongated coiled defibrillation electrode 21. Electrode21, illustrated in broken outline in FIG. 4, is located within thecoronary sinus and the great vein of the heart. At the proximal end ofthe lead is connector plug 23 carrying an electrical connector coupledto the coiled conductor. The coronary sinus/great vein electrode 41 maybe about 5 cm in length.

Implantable PCD 10 is shown in FIG. 4 in combination with leads 1, 7 and41, and lead connector assemblies 23, 17 and 6 inserted into connectorblock 12. Optionally, insulation of the outward facing portion ofhousing 14 of PCD 10 may be provided using a plastic coating such asparylene or silicone rubber, as is employed in some unipolar cardiacpacemakers. The outward facing portion, however, may be left uninsulatedor some other division between insulated and uninsulated portions may beemployed. The uninsulated portion of housing 14 serves as a subcutaneousdefibrillation electrode to defibrillate either the atria or ventricles.Lead configurations other than those shown in FIG. 4 may be practiced inconjunction with the present invention, such as those shown in U.S. Pat.No. 5,690,686 to Min et al., hereby incorporated by reference herein inits entirety.

FIG. 5 is a functional schematic diagram of one embodiment ofimplantable PCD 10 of the present invention. This diagram should betaken as exemplary of the type of device in which various embodiments ofthe present invention may be embodied, and not as limiting, as it isbelieved that the invention may be practiced in a wide variety of deviceimplementations, including cardioverter and defibrillators which do notprovide anti-tachycardia pacing therapies.

IMD 10 is provided with an electrode system. If the electrodeconfiguration of FIG. 4 is employed, the correspondence to theillustrated electrodes is as follows. Electrode 25 in FIG. 5 includesthe uninsulated portion of the housing of PCD 10. Electrodes 25, 15, 21and 5 are coupled to high voltage output circuit 27, which includes highvoltage switches controlled by CV/defib control logic 29 via control bus31. Switches disposed within circuit 27 determine which electrodes areemployed and which electrodes are coupled to the positive and negativeterminals of the capacitor bank (which includes capacitors 33 and 35)during delivery of defibrillation pulses.

Electrodes 2 and 3 are located on or in the ventricle and are coupled tothe R-wave amplifier 37, which may take the form of an automatic gaincontrolled amplifier providing an adjustable sensing threshold as afunction of the measured R-wave amplitude. A signal is generated onR-out line 39 whenever the signal sensed between electrodes 2 and 3exceeds the present sensing threshold.

Electrodes 9 and 13 are located on or in the atrium and are coupled tothe P-wave amplifier 43, which may also take the form of an automaticgain controlled amplifier providing an adjustable sensing threshold as afunction of the measured P-wave amplitude. A signal is generated onP-out line 45 whenever the signal sensed between electrodes 9 and 13exceeds the present sensing threshold. The general operation of R-waveand P-wave amplifiers 37 and 43 may correspond to that disclosed in U.S.Pat. No. 5,117,824, by Keimel et al., issued Jun. 2, 1992, for “AnApparatus for Monitoring Electrical Physiologic Signals”, herebyincorporated by reference herein in its entirety.

Switch matrix 47 is used to select which of the available electrodes arecoupled to wide band (0.5-200 Hz) amplifier 49 for use in digital signalanalysis. Selection of electrodes is controlled by the microprocessor 51via data/address bus 53, which selections may be varied as desired.Signals from the electrodes selected for coupling to bandpass amplifier49 are provided to multiplexer 55, and thereafter converted to multi-bitdigital signals by A/D converter 57, for storage in random access memory59 under control of direct memory access circuit 61. Microprocessor 51may employ digital signal analysis techniques to characterize thedigitized signals stored in random access memory 59 to recognize andclassify the patient's heart rhythm employing any of the numeroussignal-processing methodologies known to the art.

The remainder of the circuitry is dedicated to the provision of cardiacpacing, cardioversion and defibrillation therapies, and, for purposes ofthe present invention, may correspond to circuitry known to thoseskilled in the art. The following exemplary apparatus is disclosed foraccomplishing pacing, cardioversion and defibrillation functions. Pacertiming/control circuitry 63 may include programmable digital counterswhich control the basic time intervals associated with DDD, VVI, DVI,VDD, AAI, DDI and other modes of single and dual chamber pacing wellknown to the art. Circuitry 63 also may control escape intervalsassociated with anti-tachyarrhythmia pacing in both the atrium and theventricle, employing any anti-tachyarrhythmia pacing therapies known tothe art.

Intervals defined by pacing circuitry 63 include atrial and ventricularpacing escape intervals, the refractory periods during which sensedP-waves and R-waves are ineffective to restart timing of the escapeintervals and the pulse widths of the pacing pulses. The durations ofthese intervals are determined by microprocessor 51, in response tostored data in memory 59 and are communicated to pacing circuitry 63 viaaddress/data bus 53. Pacer circuitry 63 also determines the amplitude ofthe cardiac pacing pulses under control of microprocessor 51.

During pacing, escape interval counters within pacer timing/controlcircuitry 63 are reset upon sensing of R-waves and P-waves as indicatedby signals on lines 39 and 45, and in accordance with the selected modeof pacing on time-out trigger generation of pacing pulses by paceroutput circuitry 65 and 67, which are coupled to electrodes 9, 13, 2 and3. Escape interval counters are also reset on generation of pacingpulses and thereby control the basic timing of cardiac pacing functions,including anti-tachyarrhythmia pacing. The durations of the intervalsdefined by escape interval timers are determined by microprocessor 51via data/address bus 53. The value of the count present in the escapeinterval counters when reset by sensed R-waves and P-waves may be usedto measure the durations of R-R intervals, P-P intervals, P-R intervalsand R-P intervals, which measurements are stored in memory 59 and usedto detect the presence of tachyarrhythmias.

Microprocessor 51 may operate as an interrupt driven device, and may beresponsive to interrupts from pacer timing/control circuitry 63corresponding to the occurrence of sensed P-waves and R-waves andcorresponding to the generation of cardiac pacing pulses. Thoseinterrupts are provided via data/address bus 53. Any necessarymathematical calculations to be performed by microprocessor 51 and anyupdating of the values or intervals controlled by pacer timing/controlcircuitry 63 take place following such interrupts. Detection of atrialor ventricular tachyarrhythmias, as employed in the present invention,may correspond to any of the various tachyarrhythmia detectionalgorithms presently known in the art. For example, the presence of anatrial or ventricular tachyarrhythmia may be confirmed by detecting asustained series of short R-R or P-P intervals of an average rateindicative of tachyarrhythmia or an unbroken series of short R-R or P-Pintervals. The suddenness of onset of the detected high rates, thestability of the high rates, and a number of other factors known in theart may also be measured at this time. Appropriate ventriculartachyarrhythmia detection methodologies measuring such factors aredescribed in U.S. Pat. No. 4,726,380 issued to Vollmann, U.S. Pat. No.4,880,005, issued to Pless et al. and U.S. Pat. No. 4,830,006, issued toHaluska et al., all hereby incorporated by reference herein, each in itsrespective entirety. An additional set of tachycardia recognitionmethodologies is disclosed in the article “Onset and Stability forVentricular Tachyarrhythmia Detection in an ImplantablePacer-Cardioverter-Defibrillator” by Olson et al., published inComputers in Cardiology, Oct. 7-10, 1986, IEEE Computer Society Press,pages 167-170, also incorporated by reference herein in its entirety.Atrial fibrillation detection methodologies are disclosed in PublishedPCT Application Ser. No. US92/02829, Publication No. WO92/18198, byAdams et al., and in the article “Automatic Tachycardia Recognition”, byArzbaecher et al., published in PACE, May-June, 1984, pp. 541-547, bothof which are hereby incorporated by reference herein, each in itsrespective entirety.

In the event an atrial or ventricular tachyarrhythmia is detected and ananti-tachyarrhythmia pacing regimen is desired, appropriate timingintervals for controlling generation of anti-tachyarrhythmia pacingtherapies are loaded from microprocessor 51 into the pacer timing andcontrol circuitry 63, to control the operation of the escape intervalcounters therein and to define refractory periods during which detectionof R-waves and P-waves is ineffective to restart the escape intervalcounters.

Alternatively, circuitry for controlling the timing and generation ofanti-tachycardia pacing pulses as described in U.S. Pat. No. 4,577,633,issued to Berkovits et al. on Mar. 25, 1986, U.S. Pat. No. 4,880,005,issued to Pless et al. on Nov. 14, 1989, U.S. Pat. No. 4,726,380, issuedto Vollmann et al. on Feb. 23, 1988 and U.S. Pat. No. 4,587,970, issuedto Holley et al. on May 13, 1986, all of which are hereby incorporatedherein by reference, each in its respective entirety, may also beemployed.

In the event that generation of a cardioversion or defibrillation pulseis required, microprocessor 51 may employ an escape interval counter tocontrol timing of such cardioversion and defibrillation pulses, as wellas associated refractory periods. In response to the detection of atrialor ventricular fibrillation or tachyarrhythmia requiring a cardioversionpulse, microprocessor 51 activates cardioversion/defibrillation controlcircuitry 29, which initiates charging of the high voltage capacitors 33and 35 via charging circuit 69, under the control of high voltagecharging control line 71. The voltage on the high voltage capacitors ismonitored via VCAP line 73, which is passed through multiplexer 55 andin response to reaching a predetermined value set by microprocessor 51,results in generation of a logic signal on Cap Full (CF) line 77 toterminate charging. Thereafter, timing of the delivery of thedefibrillation or cardioversion pulse is controlled by pacertiming/control circuitry 63. Following delivery of the fibrillation ortachycardia therapy, microprocessor 51 returns the device to a cardiacpacing mode and awaits the next successive interrupt due to pacing orthe occurrence of a sensed atrial or ventricular depolarization.

Several embodiments of appropriate systems for the delivery andsynchronization of ventricular cardioversion and defibrillation pulsesand for controlling the timing functions related to them are disclosedin U.S. Pat. No. 5,188,105 to Keimel, U.S. Pat. No. 5,269,298 to Adamset al. and U.S. Pat. No. 4,316,472 to Mirowski et al., all of which arehereby incorporated by reference herein, each in its respectiveentirety. Any known cardioversion or defibrillation pulse controlcircuitry is believed to be usable in conjunction with variousembodiments of the present invention, however. For example, circuitrycontrolling the timing and generation of cardioversion anddefibrillation pulses such as that disclosed in U.S. Pat. No. 4,384,585to Zipes, U.S. Pat. No. 4,949,719 to Pless et al., or U.S. Pat. No.4,375,817 to Engle et al., all of which are hereby incorporated byreference herein, each in its respective entirety, may also be employed.

Continuing to refer to FIG. 5, delivery of cardioversion ordefibrillation pulses may be accomplished by output circuit 27 under thecontrol of control circuitry 29 via control bus 31. Output circuit 27determines whether a monophasic or biphasic pulse is delivered, thepolarity of the electrodes and which electrodes are involved in deliveryof the pulse. Output circuit 27 also includes high voltage switches,which control whether electrodes are coupled together during delivery ofthe pulse. Alternatively, electrodes intended to be coupled togetherduring the pulse may simply be permanently coupled to one another,either exterior to or within the interior of the device housing, andpolarity may similarly be pre-set, as in current implantabledefibrillators. An example of output circuitry for delivery of biphasicpulse regimens to multiple electrode systems may be found in U.S. Pat.No. 4,953,551, issued to Mehra, and in U.S. Pat. No. 4,727,877, both ofwhich are hereby incorporated by reference herein in its entirety.

An example of circuitry that may be used to control delivery ofmonophasic pulses is disclosed in U.S. Pat. No. 5,163,427 to Keimel,also hereby incorporated by reference herein in its entirety. Outputcontrol circuitry similar to that disclosed in U.S. Pat. No. 4,953,551to Mehra et al. or U.S. Pat. No. 4,800,883 to Winstrom, bothincorporated by reference, each in its respective entirety, may also beused in conjunction with various embodiments of the present invention todeliver biphasic pulses.

Alternatively, IMD 10 may be an implantable nerve stimulator or musclestimulator such as that disclosed in U.S. Pat. No. 5,199,428 to Obel etal., U.S. Pat. No. 5,207,218 to Carpentier et al. or U.S. Pat. No.5,330,507 to Schwartz, or an implantable monitoring device such as thatdisclosed in U.S. Pat. No. 5,331,966 issued to Bennet et al., all ofwhich are hereby incorporated by reference herein, each in itsrespective entirety. The present invention is believed to find wideapplication to any form of implantable electrical device for use inconjunction with electrical leads.

FIG. 6 is a simplified schematic view of one embodiment of animplantable medical device (“IMD”) 10 for comparison with theembodiments of the present invention.

IMD 10 is connected to heart 8 through a series of leads 16 and 18. Inthe embodiment of FIG. 6, lead 18 couples a ventricular circuit to theright ventricle; however, lead 18 could also be coupled to the leftventricle. Ventricular circuit may provide for the sensing andstimulation of the ventricle in any suitable manner as is known in theart and described above. Lead 18 may be, for example a unipolarendocardial lead as described above or any suitable lead well known inthe art. Lead 18 features two electrodes 28 and 29 at its distal end.Electrodes 28, 29 may be used for stimulation of one of the ventricles,in the case of FIG. 6, the right ventricle. In the embodiment of FIG. 6,lead 16 couples an atrial circuit to the right atrium; however, lead 16could also be coupled to the left atrium. Atrial circuit may provide forthe sensing and stimulation of the atria in any suitable manner as isknown in the art and described above. Lead 16 may be, for example, aunipolar endocardial lead as described above or any suitable lead wellknown in the art. Lead 16 features two electrodes 20 and 621 at itsdistal end. Electrodes 20, 21 may be used for stimulation of one of theatria, in the case of FIG. 6, the right atria.

Input/output circuit 54 of IMD 10 may be configured to sense cardiacactivity in each of the respective chambers and also to provideelectrical stimulation in response thereto.

FIG. 7 is a simplified schematic view of one embodiment of animplantable medical device (“IMD”) 10 in accordance with the presentinvention.

Pacing leads 16 and 18 extend from connector header module 12 to theleft and right ventricles, respectively, of heart 8. In one embodimentof the invention, leads 16, 18 are selectively insertable into connectorheader module 12 depending on the desired configuration (i.e., the leadsare inserted in one configuration to provide the embodiment of FIG. 7and in other configurations to provide other embodiments.) For example,the leads may be coupled prior to implantation. Lead 18 couples aninput/output circuit 54 of IMD 10 to the right ventricle. Input/outputcircuit 54 may provide for the sensing and stimulation of the ventriclesin any suitable manner as is known in the art and described above. Lead18 may be, for example a unipolar endocardial lead as described above orany suitable lead well known in the art. Lead 18 may comprise twoventricular electrodes 28 and 29 at its distal end. In the embodiment ofFIG. 7, electrode 29 serves as a cathode and is coupled to the rightventricle. Meanwhile, electrode 28 serves as an anode to electrode 29and is not connected with the circuit or is not in use for thisconfiguration.

Lead 16 couples input/output circuit 54 of IMD 10 to the left ventricle.Input/output circuit 54 may provide for the sensing and stimulation ofthe ventricles in any suitable manner as is known in the art anddescribed above. Lead 16 may be, for example, a unipolar endocardiallead as described above or any suitable lead well known in the art. Lead16 may comprise two atrial electrodes 20 and 21 at its distal end. Inthe embodiment of FIG. 7, electrode 21 serves as a cathode and iscoupled to the left ventricle. Meanwhile, electrode 20 serves as ananode to electrode 21 and is not connected with the circuit or is not inuse for this configuration.

Input/output circuit 54 of IMD 10 may be configured to sense cardiacactivity in each of the respective chambers and also to provideelectrical stimulation in response thereto. For example, input/outputcircuit 54 may be configured to disable connectivity of electrode 28and/connectivity of electrode 20 to accomplish the configuration shownin FIG. 7 (i.e., where electrodes 28, 20 are “not connected”). In someembodiments of the invention, the switch matrix may accomplish a switchfrom a unipolar lead configuration to a bipolar lead configuration asdescribed above. Such a switch may be accomplished using switchingtransistors and circuitry disposed within IMD 10.

FIG. 8 is a simplified schematic view of another configuration for theembodiment of IMD 10 shown in FIG. 7. With the configuration shown inFIG. 8, unipolar pacing stimulation may be delivered to the rightventricle. Additionally, sensing pulses may be delivered to either ofthe ventricles in a unipolar or bipolar fashion.

For example, in the embodiment shown in FIG. 8, the right ventricle willreceive a unipolar pacing pulse from cathode 29 while the left ventricleinto which cathode 21 has been placed will not receive a pacing pulse.That is, the pathway of current from cathode 21 may be, for example,through the heart muscle wall through the body to connector headermodule 12. In the embodiment of FIG. 8, electrode 28 is not connectedwith the circuit or is not in use for this configuration. Meanwhile,electrode 20 is also not connected with the circuit or is not in use forthis configuration.

Input/output circuit 54 of IMD 10 may be configured to sense cardiacactivity in each of the respective chambers and also to provideelectrical stimulation in response thereto. For example, input/outputcircuit 54 may be configured to route connectivity of electrode 21 toconnector header module 12 and to disable connectivity of electrode 28and/connectivity of electrode 20 to accomplish the configuration shownin FIG. 8 (i.e., where electrodes 28, 20 are “not connected”). Such aswitch may be accomplished using switching transistors and circuitrydisposed within IMD 10.

FIG. 9 is a simplified schematic view of another configuration for theembodiment of IMD 10 shown in FIG. 7. With the configuration shown inFIG. 9, unipolar pacing stimulation may be delivered to the leftventricle. Additionally, sensing pulses may be delivered to either ofthe ventricles in a unipolar or bipolar fashion.

For example, in the embodiment shown in FIG. 9, the left ventricle willreceive a unipolar pacing pulse from cathode 21 while the rightventricle into which cathode 29 has been placed will not receive apacing pulse. That is, the pathway of current from cathode 29 may be,for example, through the heart muscle wall through the body to connectorheader module 12. In the embodiment of FIG. 9, electrode 28 is notconnected with the circuit or is not in use for this configuration.Meanwhile, electrode 20 is also not connected with the circuit or is notin use for this configuration.

Input/output circuit 54 of IMD 10 may be configured to sense cardiacactivity in each of the respective chambers and also to provideelectrical stimulation in response thereto. For example, input/outputcircuit 54 may be configured to route connectivity of electrode 21 toconnector header module 12 and to disable connectivity of electrode 28and/connectivity of electrode 20 to accomplish the configuration shownin FIG. 9 (i.e., where electrodes 28, 20 are “not connected”). Such aswitch may be accomplished using switching transistors and circuitrydisposed within IMD 10.

FIG. 10 is a simplified schematic view of another configuration for theembodiment of IMD 10 shown in FIG. 7. With the configuration shown inFIG. 10, bipolar pacing stimulation may be achieved in both ventricularchambers, with delivery from the right to the left ventricle.Additionally, sensing pulses may be delivered to either of theventricles in a unipolar or bipolar fashion.

Pacing leads 16 and 18 extend from connector header module 12 to theleft and right ventricles, respectively, of heart 8. In one embodimentof the invention, leads 16, 18 are selectively insertable into connectorheader module 12 depending on the desired configuration (i.e., the leadsare inserted in one configuration to provide the embodiment of FIG. 10and in other configurations to provide other embodiments.) For example,the leads may be coupled prior to implantation. Lead 18 couples aninput/output circuit 54 of IMD 10 to the right ventricle. Input/outputcircuit 54 may provide for the sensing and stimulation of the ventriclesin any suitable manner as is known in the art and described above. Lead18 may be, for example a unipolar endocardial lead as described above orany suitable lead well known in the art. Lead 18 may comprise twoventricular electrodes 28 and 29 at its distal end. In the embodiment ofFIG. 10, electrode 21 serves as a cathode and is coupled to the leftventricle. Meanwhile, electrode 29 serves as an anode to electrode 21and is coupled to the right ventricle while electrode 20 serves tocomplete the circuit to electrode 29. Finally, electrode 28 is notconnected with the circuit or is not in use for this configuration.

Input/output circuit 54 of IMD 10 may be configured to sense cardiacactivity in each of the respective chambers and also to provideelectrical stimulation in response thereto. For example, input/outputcircuit 54 may be configured to route connectivity of electrode 20 toelectrode 29 and to disable connectivity of electrode 28 to accomplishthe configuration shown in FIG. 9 (i.e., where electrode 28 is “notconnected”).

FIG. 11 is a simplified schematic view of another configuration for theembodiment of IMD 10 shown in FIG. 7. With the configuration shown inFIG. 11, bipolar pacing stimulation may be achieved in both ventricularchambers, with delivery from the left to the right ventricle.Additionally, sensing pulses may be delivered to either of theventricles in a unipolar or bipolar fashion.

In the embodiment of FIG. 11, electrode 29 serves as a cathode and iscoupled to the right ventricle. Meanwhile, electrode 21 serves as ananode to electrode 29 and is coupled to the left ventricle whileelectrode 28 serves to complete the circuit to electrode 21. Finally,electrode 20 is not connected with the circuit or is not in use for thisconfiguration.

Input/output circuit 54 of IMD 10 may be configured to sense cardiacactivity in each of the respective chambers and also to provideelectrical stimulation in response thereto. For example, input/outputcircuit 54 may be configured to route connectivity of electrode 28 toelectrode 21 and to disable connectivity of electrode 20 to accomplishthe configuration shown in FIG. 11 (i.e., where electrode 20 is “notconnected”).

As can be seen from the above, the configurations of the electrodes 20and 28 which are not directly connected to the heart, and of electrodes21 and 28 disposed in opposing ventricles of the heart, are switchable.Moreover, the polarity of various electrodes is selectable orswitchable. In the embodiments described in FIGS. 6-10, the leadsemployed are unipolar. In alternate embodiments of the invention,bipolar leads may be employed as well. Additionally, electrodes 20, 21and electrodes 28, 29 may be similarly disposed in opposing atria of theheart.

FIG. 12 shows one embodiment of a method for stimulating a heart inaccordance with the teachings of the present invention. As discussedabove, the method of the present invention may be performed under thecontrol of any appropriate computer algorithm stored in a memory or aportion of a memory of microcomputer 58 in IMD 10. Such a computeralgorithm may be any program capable of being stored in an electronicmedium such as, by way of example only, RAM 68 or ROM 70 of IMD 10,where the contents of RAM 68 and ROM 70 may be accessed and consequentlyexecuted by microprocessor 64/microcomputer 58.

As shown at block 710, it may be determined which chamber of a left anda right chamber of heart 8 requires the higher threshold pacing pulse.This determination may be made for example, by comparing the requiredthreshold pacing pulse for the right atrium to the required thresholdpacing pulse for the left atrium and vice versa. Alternatively, therequired threshold pacing pulse for the right ventricle may be comparedto the required threshold pacing pulse for the left ventricle and viceversa.

The cathode may be assigned to the chamber that requires the higherthreshold. In some embodiments of the invention, threshold measurementsare taken and the chamber requiring higher threshold pacing pulses isautomatically assigned the cathode. This assignment may be madeautomatically, for example by a computer algorithm and/or programcapable of being stored in an electronic medium such as, by way ofexample only, RAM 68 or ROM 70 of IMD 10, where the contents of RAM 68and ROM 70 may be accessed and consequently executed by microprocessor64/microcomputer 58. Alternatively, a physician may manually assign thecathode.

Once the cathode has been assigned, the method of the present inventionmay proceed according to two paths such as, for example, those shown inFIG. 12. In the first path, beginning at block 720, the electrode in theleft chamber is assigned as the cathode. At block 730, the electrode inthe right chamber is then assigned as the anode. At block 740, it isdetermined whether the stimulation pulse will be a pacing or a sensingpulse. At block 750, it is determined whether the cathode will act as aunipolar electrode or as a bipolar electrode. If, as seen at block 752,the cathode will act as a unipolar electrode, a single pulse will beadministered from the cathode to tissue within the left chamber. If, asseen at block 754, the cathode will act as a bipolar electrode, a singlepulse will be administered from the cathode to the anode, thussimultaneously administering stimulation to tissue in both the left andthe right chambers.

In the second path, beginning at block 725, the electrode in the rightchamber is assigned as the cathode. At block 735, the electrode in theleft chamber is then assigned as the anode. At block 745, it isdetermined whether the stimulation pulse will be a pacing or a sensingpulse. At block 755, it is determined whether the cathode will act as aunipolar electrode or as a bipolar electrode. If, as seen at block 757,the cathode will act as a unipolar electrode, a single pulse will beadministered from the cathode to tissue within the right chamber. If, asseen at block 759, the cathode will act as a bipolar electrode, a singlepulse will be administered from the cathode to the anode, thussimultaneously administering stimulation to tissue in both the left andthe right chambers.

In some embodiments of the invention, the pacing mode may determine inwhich direction the stimulus is administered, i.e., whether thestimulation is administered from the right atrium to the left atrium orfrom the left atrium to the right atrium, the right ventricle to theleft ventricle or from the left ventricle to the right ventricle. Themode may further determine the type of sensing configuration of theelectrodes. Table 2 lists some examples of modes, the resultingdirection of the stimulation pulse, and the resulting sensingconfiguration of the electrodes.

TABLE 2 MODE SENSING PACING PULSE DELIVERED V₂V₂| Bipolar Unipolarbipolar sensing stimulation delivered (FIG. 7) from left electrode toleft ventricle AND right electrode to right ventricle unipolar pacingstimulation delivered from left electrode to left ventricle and rightelectrode to right ventricle V₁V₁| Unipolar Unipolar unipolar sensingstimulation delivered (FIG. 8) from right electrode to right ventricle(unused electrode is routed to pacemaker can) unipolar pacingstimulation delivered from right electrode to right ventricle (unusedelectrode is routed to pacemaker can) V₁V₁| Unipolar Unipolar unipolarsensing stimulation delivered (FIG. 9) from left electrode to leftventricle (unused electrode is routed to pacemaker can) unipolar pacingstimulation delivered from left electrode to left ventricle (unusedelectrode is routed to pacemaker can) V₁₂V₁₂| bipolar bipolar bipolarsensing stimulation delivered (FIG. from right electrode to leftventricle 10) bipolar sensing stimulation delivered from right electrodeto left ventricle V₂₁V₂₁| bipolar bipolar bipolar sensing stimulationdelivered (FIG. from left electrode to right ventricle 11) bipolarsensing stimulation delivered from left electrode to right ventricle

In some embodiments of the invention, once the proper polarities andelectrode assignments of the leads have been established, bipolarstimulation may proceed in a first direction, i.e., from a firstopposing chamber to a second opposing chamber. For example, stimulationmay proceed from the left ventricle to the right ventricle. In suchcases, simultaneous pacing stimulation occurs.

Alternatively, some embodiments may provide unipolar stimulation. Insome embodiments, a unipolar stimulation pulse may be delivered in eachchamber and followed very quickly by one or more successive stimulationpulses. The successive stimulation pulse may be administered for exampleany suitable time after the first pulse, for example from 0 to 100msecs, 10 to 90 msecs, 20 to 80 msecs or 30 to 70 msecs after the firststimulation pulse is administered. Such staggered stimulation permitsthe induced contractions of the opposing chamber to be optimized from ahemodynamic perspective. That is, pumping efficiency and output of theheart may be increased by use of slight inter-chamber timing delaysbetween two opposing chambers of heart 8, such as between the twoventricles or between the two atria.

FIG. 13 shows another embodiment of a method for stimulating a heart inaccordance with the teachings of the present invention. As discussedabove, the method of the present invention may be performed under thecontrol of any appropriate computer algorithm stored in a memory or aportion of a memory of microcomputer 58 in IMD 10. Such a computeralgorithm may be any program capable of being stored in an electronicmedium such as, by way of example only, RAM 68 or ROM 70 of IMD 10,where the contents of RAM 68 and ROM 70 may be accessed and consequentlyexecuted by microprocessor 64/microcomputer 58.

As seen at block 805 and described above, the opposing chambers of theheart in which the electrodes are to be disposed is selected. At leastone first electrode and at least one second electrode may be disposed inthe selected opposing chambers of the heart. For example, the right andleft atria may be selected or the right and left ventricles.

As seen at block 810 and described above, a type of pulse may beselected. For example a pacing pulse or a sensing pulse may be selected.

At block 820, a desired electrode configuration is determined based onthe type of stimulation desired. For example, the electrodeconfiguration may result in unipolar pacing of the left or rightventricle, unipolar sensing of the left or right ventricle, bipolarpacing of the left or right ventricle, bipolar sensing of the left orright ventricle, unipolar pacing of the left or right atria, unipolarsensing of the left or right atria, bipolar pacing of the left or rightatria, bipolar sensing of the left or right atria.

At block 830 an appropriate cathode is selected based on the desiredelectrode configuration and at block 840 an appropriate anode isselected based on the desired configuration. For example, in FIG. 8,electrode 29 is the cathode and electrode 28 is the anode resulting inan electrode configuration which delivers unipolar pacing of the rightventricle. In FIG. 9, electrode 21 is the cathode and electrode 20 isthe anode resulting in an electrode configuration that delivers unipolarpacing of the left ventricle.

An additional parameter may be selected at block 850 to determine thedirection of the stimulus being delivered. For example, In FIG. 10,electrode 21 is the cathode and electrode 29 is the anode resulting inan electrode configuration that delivers bipolar pacing from the rightto the left ventricle. In FIG. 11, electrode 29 is the cathode andelectrode 21 is the anode resulting in an electrode configuration thatdelivers bipolar pacing from the left to the right ventricle. Otherelectrode configurations are possible, including corresponding sensingunipolar and bipolar electrode configurations.

At block 860, the timing of the stimulation may be selected. Forexample, the electrodes may deliver simultaneous stimulation orstaggered stimulation.

At block 870, the stimulation pulse is delivered. More than one pulsemay be delivered based on selections made in the preceding steps.

In the embodiment of the invention seen in FIGS. 6 through 13, theparameters determined include: pacing of the right atrium, sensing ofthe right atrium, pacing of the left atrium, sensing of the left atrium,pacing of the right ventricle, sensing of the right ventricle, pacing ofthe left ventricle, sensing of the left ventricle, bipolar stimulationor unipolar stimulation, simultaneously delivered pulses or pulsesdelivered in a staggered fashion. One or any suitable combination ofthese parameters may be varied in accordance with the present invention.Alternatively, one or more of these parameters may be set at a desiredvalue while one or more other parameters are varied in accordance withthe present invention. Moreover, although the parameters are shown asbeing determined in a given order, these parameters may be determined inany combination and in any order in accordance with the presentinvention.

The preceding specific embodiments are illustrative of the practice ofthe invention. It is to be understood, therefore, that other expedientsknown to those skilled in the art or disclosed herein, may be employedwithout departing from the invention or the scope of the appendedclaims. For example, the present invention is not limited to a methodfor increasing a pacing parameter of a mammalian heart. The presentinvention is also not limited to the increase of pacing parameters, perse, but may find further application as a measuring means. The presentinvention further includes within its scope methods of making and usingthe measurement means described hereinabove. In the claims,means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures. Thus, although anail and a screw may not be structural equivalents in that a nailemploys a cylindrical surface to secure wooden parts together, whereas ascrew employs a helical surface, in the environment of fastening woodenparts a nail and a screw are equivalent structures.

1. A method of pacing opposing chambers of a heart with a pacing system,the pacing system comprising a first bipolar medical electrical leadhaving at least one first electrode configured for positioning in afirst opposing chamber of the heart, a second bipolar medical electricallead having at least one second electrode configured for positioning ina second opposing chamber of the heart, an implantable pulse generatoroperably connected to the first and second bipolar medical electricalleads, the implantable pulse generator further comprising anhermetically sealed housing capable of serving as a can electrode, andmeans for switching electrode configurations between the first electrodeand the can electrode, between the second electrode and the canelectrode, between the first electrode and the second electrode andbetween the second electrode and the first electrode, the methodcomprising: determining a primary electrode configuration; selecting acathode from the first electrode, the second electrode and the canelectrode based on the primary electrode configuration; selecting ananode from the first electrode, the second electrode and the canelectrode based on the primary electrode configuration; delivering afirst pulse between the cathode and the anode; determining a firstthreshold of the first opposing chamber; determining a second thresholdof the second opposing chamber; and selecting the first electrode as thecathode if the first threshold is higher than the second threshold. 2.The method of claim 1, further comprising: determining an alternateelectrode configuration; selecting an alternate cathode from the firstelectrode, the second electrode and the can electrode based on thealternate electrode configuration; selecting an alternate anode from thefirst electrode, the second electrode and the can electrode based on thealternate electrode configuration; and delivering a second pulse betweenthe alternate cathode and the alternate anode.
 3. The method of claim 2,further comprising: re-selecting the cathode and the anode; delivering athird pulse between the cathode and the anode; re-selecting thealternate cathode and the alternate anode; and delivering a fourth pulsebetween the alternate cathode and the alternate anode.
 4. The method ofclaim 1, further comprising: delivering the first pulse between thecathode and the anode so that the direction of the pulse occurs from thefirst opposing chamber to the second opposing chamber.
 5. The method ofclaim 1, further comprising: delivering the first pulse between thecathode and the anode so tat the direction of the pulse occurs from thesecond opposing chamber to the first opposing chamber.
 6. The method ofclaim 1, further comprising: delivering the first pulse between thecathode and the anode in a first direction; and delivering at least onesubsequent pulse between the cathode and the anode in the firstdirection.
 7. The method of claim 1, further comprising: delivering thefirst pulse from the cathode; and simultaneously delivering a secondpulse from the anode.
 8. The method of claim 1, further comprisingsensing a signal from the heart via at least one of the first electrodeand the second electrode.
 9. A computer usable medium including aprogram for opposing chambers of a heart with a pacing system, thepacing system comprising a first unipolar medical electrical lead havingat least one first electrode configured for positioning in a firstopposing chamber of the heart, a second unipolar medical electrical leadhaving at least one second electrode configured for positioning in asecond opposing chamber of the heart, an implantable pulse generatoroperably connected to the first and second unipolar medical electricalleads, the implantable pulse generator further comprising anhermetically sealed housing capable of serving as a can electrode, andmeans for switching electrode configurations between the first electrodeand the can electrode, between the second electrode and the canelectrode, between the first electrode and the second electrode andbetween the second electrode and the first electrode, the programcomprising: computer program code that determines a primary electrodeconfiguration; computer program code that selects a cathode from thefirst electrode, the second electrode and the can electrode based on theprimary electrode configuration; computer program code that selects ananode from the first electrode, the second electrode arid the canelectrode based on the primary electrode configuration; computer programcode that delivers a first pulse between the cathode and the anode;computer program code that determines a first threshold of the firstopposing chamber; computer program code that determines a secondthreshold of the second opposing chamber; and computer program code thatselects the first electrode as the cathode if the first threshold ishigher than the second threshold.
 10. The program of claim 9, furthercomprising: computer program code that determines an alternate electrodeconfiguration; computer program code that selects an alternate cathodefrom the first electrode, the second electrode and the can electrodebased on the alternate electrode configuration; computer program codethat selects an alternate anode from the first electrode, the secondelectrode and the can electrode based on the alternate electrodeconfiguration; and computer program code that delivers a second pulsebetween the alternate cathode and the alternate anode.
 11. The programof claim 10, further comprising: computer program code that re-selectsthe cathode and the anode; computer program code that delivers a thirdpulse between the cathode and the anode; computer program code thatre-selects the alternate cathode and the alternate anode; and computerprogram code that delivers a fourth pulse between the alternate cathodeand the alternate anode.
 12. The program of claim 9, further comprising:computer program code that delivers the first pulse between the cathodeand the anode so that the direction of the pulse occurs from the firstopposing chamber to the second opposing chamber.
 13. The program ofclaim 9, further comprising: computer program code that delivers thefirst pulse between the cathode and the anode so that the direction ofthe pulse occurs from the second opposing chamber to the first opposingchamber.
 14. The program of claim 9, further comprising: computerprogram code that delivers the first pulse between the cathode and theanode in a first direction; and computer program code that delivers atleast one subsequent pulse between the cathode and the anode in thefirst direction.
 15. The program of claim 9, further comprising:computer program code that delivers the first pulse from the cathode;and computer program code that simultaneously delivering a second pulsefrom the anode.
 16. A computer usable medium including a program foropposing chambers of a heart with a pacing system, the pacing systemcomprising a first bipolar medical electrical lead having at least onefirst electrode configured for positioning in a first opposing chamberof the heart, a second bipolar medical electrical lead having at leastone second electrode configured for positioning in a second opposingchamber of the heart, an implantable pulse generator operably connectedto the first and second bipolar medical electrical leads, theimplantable pulse generator further comprising an hermetically sealedhousing capable of serving as a can electrode, and means for switchingelectrode configurations between the first electrode and the canelectrode, between the second electrode and the can electrode, betweenthe first electrode and the second electrode and between the secondelectrode and the first electrode, the program comprising: computerprogram code that determines a primary electrode configuration; computerprogram code that selects a cathode from the first electrode, the secondelectrode and the can electrode based on the primary electrodeconfiguration; computer program code that selects an anode from thefirst electrode, the second electrode and the can electrode based on theprimary electrode configuration; computer program code that delivers afirst pulse between the cathode and the anode; computer program codethat determines a first threshold of the first opposing chamber;computer program code that determines a second threshold of the secondopposing chamber; and computer program code that selects the firstelectrode as the cathode if the first threshold is higher than thesecond threshold.